INTRODUCTORY ESSAY. 77 The whole of Continental India lies north of the equator, and considerably more than half of its area north of the Tropic of Cancer, whose position very nearly corresponds \vith the hase of the peninsula of Hindostan. Proceeding northwards from the tropic, there is no sea nearer than the Arctic Ocean; but as we advance towards the equator the width of the land gradually diminishes both in the Madras and Malayan peninsulas. It may be observed also, that due south of India, the ocean extends without interruption be- yond the Antarctic Circle, while to the eastward, not only on the equator but in the southern hemisphere, there is much land. The • Eastern Archipelago, from consisting of Hrge islands, separated by belts of s'ca, possesses a humid and equable climate; but the great continent of Australia, being a vast expanse of low land, becomes enormously heated when the sun is in the southern hemisphere, and presents extremes of climate. To the westward the coast-line of Beluchistan continues somewhat north of the tropic till it enters the Per- sian Gulf; but the great continent of Arabia advances far within the tropic; while, a little further west, Africa extends, uninterrupted by sea, far into the south temperate zone. From ibis relative position of land and sea, it is evident that the whole of the rain which falls in India must be derived from the southward or eastward, and that those parts only can be subject to heavy rains, towards winch the sea-wind blows. The maps of the monthly isotheruials*, recently published by Dove, enable us to trace with considerable accuracy the periodical changes of temperature throughout India and the neighbouring countries. An inspection of these maps shows us that iii January the isothermal imes in the northern he- misphere arc nearly parallel to the equator, but that, in the southern, Africa and Australia arc pvctcrnaturalljo hot. Till the vernal equinox, the equator of heat (or that line from which the temperature diminishes both towards the north awl towards the south) lies south of the terrestrial equator; but Tsothewuals appondul to this Kssio.